The invention concerns a method of and device for obtaining short shavings trimmed from the seams inside longitudinally welded pipes.
When pipes are welded with longitudinal seams, and especially when strips of steel are shaped with rollers or cages for example into a cylinder with a longitudinal seam that must be welded tight, the pressure exerted on the weld by the edges of the strip leaves a bead of expressed and solidified molten metal along the seam on both the inner and outer surface of the pipe.
This material is ordinarily removed from inside and outside the pipe by trimming tools that follow the welding point. The particles removed in the outer trimming process are relatively easy to handle. They are accessible enough and have enough free space around them to be transferred to scrap baskets, chopped short, and removed or simply conveyed along gutters to a chopping station.
The shaving removed by the inside trimming process, however, remains inside the pipe in the form of a long and continuous strip.
The lengthy shaving not only entails drawbacks during the subsequent cutting of the "endless" billet into sections due to increased wear on the saw blade as the result of sudden and irregular stress on the teeth but also slides part-way out of the sections as they are removed to one side, hanging from their ends and endangering the personnel in the immediate vicinity. The lengthy shaving is also very difficult to remove with high-pressure water or long-shafted brushes.
Proposals have been advanced to eliminate these drawbacks by notching the inside bead before trimming it in order to obtain a shaving that is either already broken up or easy to break up. The notching rollers employed for this purpose, however, can damage the inner surface of the pipe and even produce incisions deep enough to make the pipe wall too thin in the vicinity of the seam, eventually resulting in stress peaks and decreasing fatigue strength when pressure is applied to the inside of the installed pipe.
German Application 3 219 369 discloses a method of and device for obtaining short shavings. The trimmed-off shaving exerts a transverse force that produces torque on a tool holder and hence on cutters mounted on the holder at an angle. The cutters are mounted adjacent and overlapping and accordingly generate short individual shavings.
Since, however, stress peaks are known to occur when inside shavings are trimmed from hot-working steels in particular while the cutter is entering or leaving the work, the inside edging bead in this case, the method disclosed in the aforesaid document results in excessive downtime due to the constant need to replace the cutters.
Furthermore, the transverse forces needed to maintain rotation result in reaction forces on the trimming tool that, since the tools are usually mounted at the ends of relatively long shafts, make them vibrate transversely and hence trim irregularly.